The long term objective of this research is to understand the cellular mechanisms underlying the embryonic development of the stereotyped cellular pattern in the central nervous system. The complexity of trying to understand the processes of cell determination during the development of the vertebrate central nervous system in terms of specific cell lineages and cell interactions, makes the reductionist approach of choosing a simple system quite attractive. It is hoped that this approach will reveal fundamental principles common to all organisms, but might be masked and are certainly much more difficult to study in more complex species. The early embryonic development of the insect central nervous system is in many respects remarkably similar to vertebrate neurogenesis. The grasshopper embryo in particular is an attractive preparation in which to study these question because the neuroepithelium is very thin and highly transparent; the cells are relatively large, highly accessible, and can be individually identified from birth to maturation; and the pattern of precursors and their progeny is relatively simple and highly stereotyped. A variety of cellular techniques will be used to study the roles of cell lineage and cell interaction in the determination of both individual neuronal precursor cells, and their individual neuronal progeny. In particular, the study will focus on the spatial and temporal pattern of regulation versus cell autonomy. The neuroepithelial cells along the dorsal midline (a relatively simple two dimensional sheet of five precursor cells and their progeny) will be manipulated using laser ablations, the embryos grown in culture, and the cells assayed using a variety of lineage and morphology markers via intracellular injections, immunocytochemistry using serum and monoclonal antibodies, and electron microscopy.